The present invention relates to bearings for supporting a shaft in sliding and/or rotary motion; more particularly, to a journal bearing for supporting a reciprocable pintle in a pintle-type valve; and most particularly to a modular bearing assembly wherein two independent bearings are each radially compliant and also form redundant axial seals against leakage of a fluid, especially a gas, through the assembly.
Linear and rotary actuators are commonly employed in various automotive, chemical, and general industrial applications for regulating gas flow and other similar functions. Many newer applications have very stringent requirements with respect to shaft leakage past a journal bearing. Some of these applications, such as fuel cells, are intolerant of any shaft leakage because the managed medium, such as hydrogen, is highly volatile and explosive. Control valves in such applications require substantially perfect axial alignment of the metering orifice and the valve shaft or pintle to close completely and reliably. Such alignment is difficult if not impossible to achieve in known control valves, especially in valves which must operate satisfactorily over a wide range of temperatures and pressures, with attendant thermally and torsionally induced dimensional changes in valve components.
The resultant misalignment inherent in known gas management valves not only makes it difficult to meet the valve leakage requirement but also diminishes valve performance by introducing significant parasitic frictional forces that are the direct result of component misalignment. To account for these frictional forces, actuators commonly are oversized, the result being devices which may be bulkier, heavier, and costlier than required for the gas management function alone. In automotive applications, for example, such oversized actuators can add to the weight of a vehicle, incurring permanent cost in reduced fuel efficiency and increased brake wear. Excess vehicle weight may increase to the point at which a given vehicle must be reclassified to a heavier, bigger class, incurring additional insurance cost and government imposed penalties.
What is needed is a modular assembly of a bearing which is readily pre-assembled offline, in which the bearing is radially compliant and may be self-aligned by the pintle, and in which the bearing also functions as a shaft seal.
The present invention is directed to an improved modular journal-type bearing assembly comprising two bearing elements retained in a housing and positively loaded in opposing axial directions by a compression spring disposed therebetween. An operative shaft to be both supported and sealed against leakage by the bearing, for example, a valve pintle shaft, is disposed in an axial bore in each of the bearing elements, the bores preferably being as closely fitted to the diameter of the shaft as is possible without causing the shaft to bind in the bores. Each of the radial bearing faces opposite the spring forms a seal with a corresponding radial surface of the housing, defining thereby a redundant sealing system. The bearings are free to move radially within the housing by a predetermined small distance to allow the shaft to be operatively self-centered, such as by an attached valve head mating into a valve seat. The improved bearing assembly may be pre-assembled offline to facilitate its incorporation into an apparatus, for example, a pintle valve, and may also be retrofitted into existing bearing installations.